Long Term Evolution (LTE) wireless communication networks developed by members of the 3rd-Generation Partnership Project (3GPP) use orthogonal frequency-division multiplexing (OFDM) in the downlink and Discrete Fourier Transform spread (DFT-spread) OFDM (also referred to as single-carrier frequency-division multiple access, or SC-FDMA) in the uplink. The basic LTE downlink physical resource can thus be seen as a time-frequency grid as illustrated in FIG. 1, where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval. The uplink subframe has the same subcarrier spacing as the downlink and the same number of SC-FDMA symbols in the time domain as OFDM symbols in the downlink.
In the time domain, LTE downlink transmissions are organized into radio frames of 10 milliseconds (ms), each radio frame consisting of ten equally-sized subframes of length Tsubframe=1 ms, as shown in FIG. 2. For normal cyclic prefix, one subframe consists of 14 OFDM symbols. The duration of each symbol is approximately 71.4 microseconds (μs).
While the development and deployment of LTE networks provides users with greatly increased wireless data rates and has enabled the development of a wide variety of mobile broadband (MBB) services, demand for these services continues to grow. In addition to this increased demand for improved bandwidth and performance, new applications for special-purpose devices, such as machine-to-machine (M2M) devices in machine type communications (MTC), continue to be developed. One of the issues with the existing LTE standard is that it uses a fixed large-sized subframe structure, which results in resource wastage for very small-sized data as is often the case in critical MTC (C-MTC) scenarios.
Accordingly, new radio access technologies are currently under development for a future generation of cellular networks, which may be referred to as “5G” networks. This new development is geared towards fulfilling a wide range of varying requirements including latency, reliability and throughput. 5G is envisioned not only to expand MBB service performance, as in 4G, but also to address a wider range of use cases and enable a fully networked society. These goals are discussed, for example, in Osseiran, A., et al., “The Foundation of the Mobile and Wireless Communications System for 2020 and Beyond: Challenges, Enablers and Technology Solutions,” in Vehicular Technology Conference (VTC Spring), 2013 IEEE 77th, vol., no., pp. 1-5, 2-5 Jun. 2013.
A subset of 5G design targets includes the support of 1000-times more data traffic, 10 to 100-times higher number of connected devices, 5-times reduced end-to-end latency, and a higher degree of reliability and availability with respect to today's wireless networks. Proposed adaptations include, for example, using different subcarrier spacing as well as smaller and variable sized subframes in mixed mode operation. There is a consensus on the three fundamental enablers to reach 5G targets: more spectrum, denser base station deployment, and better transmission technology.
In standardization efforts by 3GPP, work has been ongoing to study the feasibility of using a pre-scheduled uplink resource to reduce latency. A drawback with allocating pre-scheduled time-frequency resources to wireless devices is that there is no way for the system to know before-hand whether the resources will be utilized or not. This may lead to poor resource utilization and restrict the network in dynamically prioritizing resources. One way to improve the utilization is to pre-assign a given time-frequency resource to multiple users, thereby creating a contention channel between the assigned users. This approach, however, still does not enable user prioritization, nor does it facilitate dynamic scheduling of the time-frequency resource to a different user. Accordingly, improved techniques for efficient utilization of low-latency uplink resources are needed.